Does anyone else have any personal experience with this power?
Yes. Usually our ranger uses it after even damage is announced, because we roll attack and damage at the same time (i.e. put all the dice in the dice cup). No problem at all.
Does anyone else have any personal experience with this power?
The problem here, as I see it is the DM being a little over zealous in his efficiency of action. (obviously a case of ZOMBIE SMASH Syndrome).
Seeing as the DM knows that there is a potential interrupt (encounter) power out there he should not try and do everything at the same time, and show a little more consideration to his players.
It doesn't really slow the game down (and is general good practice) to:
1: declare attack clearly
2: make attack roll and determine hit/miss
3: determine damage
This is three clear steps in resolution, and the player who has the interrupt should be alert enough to speak up. In this case when the attack is declared.
In my group I have a ranger that has a reaction to shift away when a creature moves adjacent. As I know this whenever I move a creature adjacent to him I look at him and say "reaction?" he says yes or no and I continue. It really doesn't slow the game down because we are both used to it.
All it takes is a little consideration, co-operation and common sense.
I specifically mean powers that require a new decision point to be added to game where there was none before.You do just mean Immediate Interrupt powers, right? Not Immediate Reaction powers and Immediate Interrupt features such as Combat Challenge?
Actually, as a DM you should know your PC´s AC.I think the mistake here is in the way the DM is checking if there was a hit.
Rather than asking "Does an 18 hit your AC", my DM would ask "What is your AC?" The subtle difference here is that it gives a player a chance to jump in before a hit is calculated, allowing both the PC and DM to set a pace for the battle. Even if the DM had already announced a hit, the PC doesn't generally know by how much the hit happened. That make it harder to meta-game the power if the trigger is "on attack" and he had already rolled. Finally, it makes retroactively changing the result easier and less painful, since it's less resolved.
As an aside, I don't have a problem with the PC seeing the roll. It adds some tactical value to using Immediate Interrupts, depending on the effect. I'm most familiar with Shield, and the roll adds a certain amount of decision-making. On a 19, chances are I'll have to take the hit; on a 12 it's a little more of a gamble, and on a 2... well, if I'm getting hit on a 2, I may be screwed anyway.
Actually, as a DM you should know your PC´s AC.
Indeed, the DM should know the PC's standard AC. But with power bonuses, Second Wind, Total Defense, and feats (e.g., Shield the Fallen, Sideways Defense), AC will often deviate from that standard value. As such, I almost feel like the DM should let the player track AC and inquire at the time of the attack, every time. Otherwise, the DM will forget about the adjustments and the feats will become useless in actual play.
This is my biggest problem with 4e -- so many things to track, it's too much for mortal brains.